1. Field of Invention
This invention relates to a system of annular circular pedestal rings for heavy cranes and lifting devices. Specifically, the invention describes a system of multiple concentric pedestal rings to provide increased strength and stability for a ring supported crane.
2. Related Art
For purposes of clarity, it is understood that the term "ring", unless otherwise specified, is used in this description and specification to refer to ground supported annular pedestal support rings as used in heavy cranes and similar lifting devices. These rings are supported by a plurality of pedestals, which transfer weight loads to the ground.
Ring supported lift cranes have been known in the field of heavy lifting for many years. Many such cranes are modified mobile track crawler cranes, while others are site erected fixed cranes or barge mounted marine heavy lift cranes. All types of ring supported lift cranes are based on the same physical principal of weight transfer of the boom, load, crane upper and lower works and counterweight to the ring footprint.
Typically, the crane upper works and lower works fit within the ring, with the lower works connected to the ring through a roller path for rotation. The upper works typically include the cab, engine, load lifting power transmission and winch drums. Attached to one end of the upper works is a boom foot carrier supporting the pivotally mounted boom and/or mast. At the other end of the upper works is the counterweight carrier. The upper and lower works are concentric with the ring, and rotate with respect to the lower works about a generally vertical swing axis. The weight of the counterweights, boom, mast and load is supported by rollers mounted to the upper works. These rollers are supported by and move over the ring. The ring is supported by a plurality of pedestals, which may be integral and attached to the ring, that transfer the total weight to the ground.
Prior art cranes utilize a single ring. Rings are traditionally constructed in segments, typically eight, to form together into a complete ring by pinned connections.
These segments mate to form one ring diameter to form a curved beam. A rail formed from a relatively thin steel plate cut to the radius of the ring is then placed on top of the ring to form a smooth surface on which the rollers move.
The amount of weight that can be supported by the ring is dependent on the strength of the curved beam, strength of the pedestals and the number and placement of pedestals.
A significant limiting factor is the number and placement of the pedestals. Additional pedestals afford additional means of transferring weight load to the ground, reducing bending moments in the ring. These additional pedestals are limited by spatial constraints below the ring, where a limited amount of room is available. Further, the addition of pedestals does not decrease the direct vertical load force placed on a pedestal by the crane.
Another significant limiting factor of the load capacity of the ring system is the strength of the curved beam. To increase the strength of the beam, a new set of heavier segments must be used. These segments are expensive, difficult to maneuver, and are typically unique to a particular crane design.
It would therefore be a new and useful improvement of the prior art for a pedestal ring system of a heavy crane or lifting device to not be limited in capacity by the strength of its rollers, roller path, ring system and pedestals, but for additional load capacity to be provided by distributing these loads through to multiple concentric rings.